Project Abstract The long term goal of this project is to identify the mechanisms whereby recombinant vault nanoparticles, engineered to contain immunogenic peptides, generate innate and adaptive immune responses. There are few licensed vaccines for protection against infections in mucosal tissues, namely because we lack an understanding for designing vaccines that induce mucosal immunity. We hypothesize that the hollow, recombinant vaults, the size of small microbes, could be engineered to induce mucosal immunity and be used as a tool to identify key immune triggers which produce Th1 cells that traffic to genital mucosal tissue (GT).We chose infection by the pathogen, Chlamydia trachomatis, which relies on Th1 mucosal immune responses for elimination, is a significant burden on health care, and for which there is no effective vaccine. C. trachomatis is a prominent cause of sexually transmitted infection (STI) and instigator of female reproductive dysfunction, with over 1 million cases in the U.S. annually. Vaginal delivery of the mouse-adapted strain of C. trachomatis, C. muridarum, induces an STI similar to human chlamydial STI and can be prevented by the presence of Th1 within vaginal tissues. We have shown that vault vaccines interact with and active innate immune cells, which further reshape adaptive immune responses downstream. Vaults are unique in that they are natural nanoparticles with self-adjuvant properties. In this proposal we will take advantage of mosaic vaccine design and investigate how vault nanoparticles engineered to contain chlamydial proteins induce immune responses and protective immunity against chlamydial genital disease in mice. In Aim a we utilize vault vaccines containing conserved region ?mosaic? MOMP sequences and a conserved PMPG region covering all common human serovars to determine optimal vaccine doses. In Aim b. we use vaults containing the analogous C. muridarum (MoPn) sequences as a ?proof of concept? test for protection against Chlamydia muridarum vaginal challenge. In Aim c. we will use vault vaccines containing mosaic MOMP sequences and a PMPG conserved region selected from human serovars at the optimal doses determined above as a ?proof concept? for protection from human Chlamydia trachomatis challenge in mice. This proposal investigates whether and how vault mosaic vaccine will provide broad and depth crossing-serovar protective immunity. Our research will shed the light on the critical issues which need answers in the current vaccinology field. These studies will be done in collaboration with Dr. Otto Yang, an expert in mosaic vaccine and Dr. Leonard Rome, an expert in vault nanoparticle technology.